The present invention relates to glass orifice nozzle arrays and methods of producing them, and more particularly to glass orifice nozzle arrays suitable for use in an ink jet printing apparatus as orifices in an orifice plate or charge plate assembly.
Ink jet printing apparatuses of the type in which the present invention is useful produce a plurality of uniform drops aligned parallel to one another and perpendicular to the movement of paper or other material upon which printing is to be effected. The printing is produced by using a reservoir of a printing fluid, such as ink, with a plurality of aligned orifices at the bottom of the reservoir. The ink is ejected through these orifices at a predetermined rate and is stimulated in such a manner that uniform drops of ink are formed at the ends of the filaments of ink which issue from the orifices. A series of charging electrodes are positioned adjacent the points of drop formation and are connected to sources of changing control voltage, so that corresponding electrical charges are induced upon the drops at their respective times of formation. The drops then pass through an electrical deflection field which causes drop deflection in correspondence with the applied changes. Drops which are uncharged may be directed into an appropriate positioned catcher. Alternatively, drops which are charged above some predetermined level may be directed into the catcher.
Economical methods of forming the orifices in an orifice plate or holes in a charge plate are difficult to find since the nature of the system requires the use of extremely small diameter holes in these plates. For example, the orifices in a typical orifice plate are generally in the range of 0.0005 to 0.0015 inches in diameter and the holes in a typical charge plate are generally in the range of from 0.005 to 0.010 inches in diameter.
It has been recognized that orifice plates for ink jet printing apparatuses may be fabricated from hollow glass capillary tubes which have been aligned to form a uniform array of orifice nozzles. For example, Cone, U.S. Pat. No. 4,112,436, teaches forming an orifice plate having glass nozzles by aligning a number of small inside and outside diameter hollow glass tubes on a glass substrate, pouring an epoxy resin around the tubes, and applying a second glass plate over the assembly to form a sandwiched block. After curing, the block is sawed orthogonally to form thin sections of glass nozzle arrays. The sections are lapped and polished and then affixed to a rigid backing plate.
Likewise, Humenik et al, U.S. Pat. No. 4,122,460 discloses forming an orifice plate using a number of hollow glass capillary tubes. The tubes are aligned on a supporting substrate, covered with a second support structure, and then clamped and positioned so that they are vertical. Solder glass is then placed in longitudinal grooves cut into the support structure, and the assembly is heated to melt the solder glass which flows by capillary action into the spaces between the tubes and seals the grooves. After cooling, the assembly is sawed into thin sections forming the nozzle arrays and then lapped and polished.
However, the use of hollow glass tubing in forming the nozzle arrays causes problems during the sawing, lapping, and polishing stages of the process. The small, deep apertures of the orifices in the nozzle array tend to collect and fill up with the debris and dust produced during the sawing, lapping, and polishing steps. Since the tubes must be completely clear of any obstructions when used in ink jet printing apparatuses, this tendency to collect debris and dust necessitates time consuming and not altogether successful cleaning operations to keep the tubes clear.
It has been proposed to place wax in the glass tubing to prevent other material from entering the tubing during processing. The wax can be removed by heating the nozzle array to above the melting point of the wax. However, it is quite difficult to get wax or other similar material into the extremely small diameter openings in the glass tubing. Moreover, it may be necessary to repeat the wax filling sequence several times during the fabrication process, especially if there are heating steps such as the melting of solder glass since the wax will tend to melt and flow out of the tubing during such steps.
Accordingly, the need exists in the art for a process for fabricating glass orifice nozzle arrays for use in ink jet printing apparatuses which avoids the problems of collection and accumulation of debris in the apertures of the nozzles.